This article is shared to better describe my version of Abbey Island from a previous thread about islands of Karameikos.

Changes to the Knights of Halav
This revision and expansion of the work of Jennifer Guerra is intended to alter the order slightly. This version does not consider the knights to be paladins. It also attempts to integrate two Dungeon magazine adventures more thoroughly into Karameikos.

Summary & Brief History
The Knights of Halav, officially the Military Order of Halav of the Golden Sword, was founded in AC 464 in the coastal regions of the Gulf of Halag to oppose extreme danger from chaotic non-human forces and to resist Darokin meddling. The order's greatest victories came fighting the chaotic forces plaguing Traladara during the Holy Wars of the 7th and early 8th century. The knights have waned in power since the Vampire Wars ended. The Order was principally a fraternal society for high-born Traladaran men when the Thyatian army invaded in AC 900. This secret society is today generally called the Order of the Golden Sword. A precious few knights bide their time, hoping for an eventual strike against Thyatian rule.

The order was established on a small island, called Abbey Isle today, in the Gulf of Halag south of the Blight Swamp. (DM only: Founded Thaumont 15th, AC 464. Great Hall completed AC 477.) The isolated location prevented the order from being infiltrated by nosferatu, vampires or lycantropes during the order's most vigorous campaigns. The order has always been commanded by a "Master." Unfortunately the perilous coasts of the gulf made continued supply to the order's great hall increasingly expensive as ships, men and supplies were lost over the centuries.
The Knights of Halav reckon the years with the old Traladaran calendar. (Add 1776 to any year and write as 2776†. It is pronounced as twenty-seven hundred and seventy-sixth year of the sword.)

The Vampire Wars and Relocation
In AC 762 the order was infiltrated by a powerful vampire and wiped out on Abbey Isle. The next year, survivors were able to storm the island and slay the unholy creatures that had taken residence. After extensive scouring of the island, it was decided that it would be abandoned by the order. The island was gifted to the Church of Traladara when the order relocated to a sylvan manor near Sisak Village along the Westron Road in AC 767. The new stone Great Hall, wooden manor house and tower was built 3 miles west-northwest of the village. (This place is now know as Night Tower. It is no longer under control of the Order of the Golden Sword.)

The Manor Today, Monoliths & The Sons of Night
Today, the tower has been repaired and is home to a conjurer named Thaddigren Dentiata and his associates. (More information can be found in Dungeon Magazine #24, "In the Dread of Night" pp. 6-24. A map of both the village and the region is provided therein. The mysterious monoliths are not shown on the map, but are nearby.) Dentiata dabbles in dark mysteries within a secret magic cult called the Sons of Night. They appear to have long existed in Traladara but have always been very limited in numbers... perhaps they are active across southeastern Brun (The Known World). It is unclear if the source of their power comes from entropic immortals or from the horrible Old Ones. Either way, if successful, things will end badly.

Decline, Catastrophe & the Resistance
This move proved ill-timed as it coincided with the famines and plagues of the 8th century AC. The order was barely able to continue. Once proud knights could be found scrounging in the fields for turnips. By the mid-9th century the order had lost its military vigor and became an fraternal organization. While ritual and ceremony flourished in the decades preceding the Thyatian Conquest, any noble of rank was admitted. The Thyatian legions marched across Traladara toward Sisak and the nearby Tower.

One young Knight of Halav, Sir Zorag Ivanov, gathered a handful of men to stage a defense of the manor. They were slaughtered, however the order had been gifted a martyr. The Great Hall and tower were razed and the manor burned to the ground. The order has not returned out of fear of discovery. The Thyatian governors outlawed the order and hunted as many as could be found.

A few knights survived the purge. The society went dark, went into hiding and changed their nature into one of national resistance. They abandoned the Tower ruins near Sisak. The Church of Traladara and the families of noble Traladaran families will often grant a hunted knight sanctuary and aide. Some of the rituals of the Cult of Halav appear to have been adopted from the Knights of Halav, but the groups are unaffiliated. As both groups are nationalists, who knows what the future holds?

Joining the Society and Strength
For practical purposes, human fighters of 2nd level or higher are considered for the order. Considering the small size of the order, they may not be especially particular about candidates assuming they trust they are not infiltrators. To qualify for membership, candidates must be Traladaran. Even false rumors of other heritage will preclude the candidate from being invited into the order. It is unclear how the order would respond if an invitation was rejected and the order's secrecy threatened. No candidate worshiping at any church but the Church of Traladara would be considered. A period of 4 to 9 months in service to a senior sponsoring knight and study of the orderly laws is typical, but not mandatory under the current weakened state of the order.
Even during the Holy Wars, this order never numbered more than 30 knights, however then they would hire men at arms and mercenaries to lead into battle. Armies of a few hundred are spoken of in hushed tones.
As a secret society, only trusted fighters would be invited after a careful vetting. Training may go on for years in secret for sleeper agents of the order. In a secret ceremony in the woodlands near Sisak, the new novice is knighted as a Knight of Halav. The laws of the order would be seen by outsiders as mystical, xenophobic and secretive. Currently the order has transformed into a nationalist opposition group accepting non-Fighters. To date, no thieves have ever been admitted. (If using such variant rules, adventurers, a thief-fighter hybrid, would be considered but unlikely to be admitted.)
Currently, the order is tiny with only 9 knights and 7 retainers. Fewer than 4 knights are likely to be found at the manor. Levels: F2, F2, F2, MU2, C3, F3, F4, F5, F5. Knights do not train squires as a historical knight would have done. Alignments tolerated are: LG, LN, LE, and N. (In a classic B/X alignment system Lawful or Neutral.) Currently only one F4 and one F3 are Lawful-Evil. The current Master is Sir Emeric Marilenev (F4), an older cousin of Lady Magda Marilenev.

Rituals
A Golden Sword: The Sword of Halav
Monoliths
Green Robes

Some induction ceremonies take place at a circle of stones near Sisak, a circle of stones near Portown and baptism in the upper waters of the Castellan River. All involve a golden sword and an officiating knight from the order.

Advantages of the Order
A primary benefit from the order is connection to the most noble of Traladaran clan families. While the common folk are dismissive of the order both due to their small numbers and antiquated views, the Traladaran nobility think the order romantic.

Benefits of the Order
+1 on all Saving Throws against Thyatians or their allies. (After 1 full level in the Order)
+1 Morale for Traladaran underlings or retainers. (After 3 full levels in the Order)

The Abbey Today
Today a small abbey is located on the island built over the ruins of the Great Hall and the dungeons that kept such dark creatures. Monks, lay persons and clerics of the Church of Traladara are relocated here as penitence for lapses of faith. Fewer than 10 persons are typically in residence... the majority are normal men, laity or monks. Rarely is a spell-casting cleric of greater than 2nd level in residence. The ranking cleric of the Church of Traladara in Portown (Port Gorod) monitors the abbey from afar. It is a thankless burden that is often neglected.
The Town Fathers and the Harbor Master of Port Gorod are interested in building a lighthouse on this island to improve their moribund mercantile trade. This is the hook for the adventure described in Dungeon Magazine #34, Isle of the Abbey.

Postscript
Portown (AKA Port Gorod)... developed from J. Eric Holmes tantalizing references to the town in 1977... is from my personal campaign. It is a coastal town of fewer than 3,000 people northwest of Halag (Fort Doom). It is well developed as a deeply conservative Traladaran town largely unaffected by the events of the last century. If a DM choose not to include Portown, substitute Halag, Fort Doom.

Sisak is a town introduced Dungeon Magazine (Issue #24, "In the Dread of Night"). It is unclear if the Sons of Night, who also rely on ritualistic stones for their ceremonies, choose the old manor by design or chance.

Bibliography
Order of the Golden Sword, by Jennifer Guerra (http://www.pandius.com/goldswrd.html)
Threshold Magazine #1 (p. 56); Integrates The Knights of Halav into the greater Mystara fan-histories.

Very interesting ideas and location!
I would probably use the adventure in Dungeon #24 for the Darkers (followers of Nyx featured also in my Koskatep dungeon in Threshold), but you made some nice connections I could use too

Thanks. I use an alternate pantheon for Karameikos. For traditional pantheons, Nyx seems a good fit for the Sons of Night.

I have a vile, mother goddess known as Grendel. (I use B/X-era gods rather than BECMI-era Immortals. I began the campaign before the change.)

I have two important groups IMC for Western Karameikos… the gnolls and a small, but magically gifted tribe of goblins, the Horrific Spawn. The story goes that about 700 years ago, the goblin shaman of the Horrific Spawn learn to summon dark, Lovecraftian monsters and thouls to do their bidding. From the power of this unique ability, they soon dominate more numerous tribes of hobgoblins and ogres of canon Mystara. In the never-ending machinations of the shaman of the Horrific Spawn, they enter into pacts with dark wizards, the Sons of Night. The Sons of Night splinter from the Horrific Spawn 500 years ago.

When the Thyatian Conquest occurs, the Horrific Spawn are reduced in numbers and go into hiding. They re-emerge and assault Luln in 974. They are once again broken. The gnoll leadership of the Blood Reavers undergo yet another schism under the charismatic gnoll-king Rashak and thus Rashak's Reavers form. The Horrific Spawn fall under this new king's banner.

I use Grendel as the entropic god revered by both goblinoids and evil humans. A the Sons of Night share a history with the goblins, they can possibly be in cahoots with one other for mutual benefit or to learn rituals from one another. As Nyx was introduced after Grendel IMC, I play Nyx as less involved in the struggles of mortals. I am uneasy as a DM with Nyx's ambitions for the mortal realm… success could derail everything. Grendel is more chaotic and simply bent on destruction.